1. Field of the Application
The present application relates to a rectifier stage of an axial turbine engine compressor, in particular a rectifier stage placed directly downstream of the input blower of a turbo-reactor or turboshaft engine compressor. The subject application also relates to a compressor comprising such a rectifier and a method for retaining blades of a rectifier stage of an axial turbine engine compressor, in particular a rectifier stage placed directly downstream of the blower at the input of a turbo-reactor or turboshaft engine compressor.
2. Description of Related Art
The first rectifier stage of a turbo-reactor or turboshaft engine must meet special requirements regarding blade resistance to the impact or intrusion of a foreign object. Indeed, in flight, turbo-reactors and turboshaft engines are likely to suck in various types of foreign objects, such as, for instance, ice or birds. The blower at the engine front is dimensioned to resist this kind of stress, but it still remains that this kind of foreign object may not be sufficiently destroyed by the blower so as to pass through the engine without causing further damage. Indeed, the rectifier stage directly downstream of the blower can also be subject to damage through this kind of foreign object. The blades of this stage may be distorted by the impact of the foreign object and possibly become dislodged, in particular at the inner shroud. A dislodged blade would cause very serious damage to the turbine engine in comparison with a foreign object of the above-mentioned kind and is by all means to be prevented. Fastening of the blades to the rectifier stage at the outer shroud is usually done by welding, riveting, or screwing. This kind of connection is rather stiff and resistant in comparison with the connection to the inner shroud, which is generally ensured by embedding or countersinking the end of the blade into some damping material. Therefore, it is necessary to use locking systems at the blade root.
GB 700,012 discloses a scheme for fastening stator blades to an outer shroud, as well as an inner shroud, wherein the ends of the blades are inserted into respective slots in the inner and outer shrouds, and wherein a wire acting as a hook is passed through openings in the ends of the blades. However, this document does not specify the length of the wire and does not specify how the wire is inserted into the openings. With regard to the teachings of this document it appears that inserting the wire into the openings of several successive blades is probably made very difficult because of the stiffness of the wire and the reduced clearance provided between the wire and the orifices.
GB 732,919 discloses a scheme for fastening stator blades similar to the preceding document. The blade tips are inserted into respective slots of the stator, and a wire acting as a lock is inserted into openings of the protruding blade tips. The openings are spaced apart from the slots, and the wire is maintained by a metal sheet solidly fastened to the stator and bent over the wire. Moreover, the blades may be spot welded to the metal sheet involved. This document does not specify the length of the wire nor the number of blades held by one wire portion. Nor does it specify how the ends of adjacent wires are joined. However, it is clear that the wire is held in place by bending the end portions of the metal sheet extending between the blades. Just like for the teachings of the preceding document it appears that inserting the wire into the openings of several successive blades is probably made very difficult because of the stiffness of the wire and the reduced clearance provided between the wire and the orifices.
EP 1 213 484 B1 also discloses a similar scheme for fastening blade tips and roots to outer and inner shrouds, wherein a strip or band is inserted into corresponding openings of the blade tips and roots.
The connecting schemes of these documents are limited to locking, i.e., preventing a blade tip or root from escaping from its respective slot. Moreover, they require a final step of fastening the wire or strip.
Although great strides have been made in the area of axial compressors, many shortcomings remain.